1. Field of the Invention
The present invention relates to a noncontacting clinical thermometer for measuring the temperature of an eardrum or a body surface as an object of temperature measurement.
2. Description of the Related Art
Conventionally, contacting clinical thermometers for measuring the skin temperature of a living body have been extensively used for general purposes. The temperature of a body surface to be measured by such a clinical thermometer is strongly influenced by an environmental temperature. Therefore, the body surface temperature is different in nature from a so-called body temperature which is used in fields of medical treatments and medical science for the purposes of screening for the presence/absence and the condition of a disease, and for the basal body temperatures of women. For this reason, it is inadequate to measure and use the skin temperature as a body temperature for these purposes.
Consequently, thermometry for an eardrum has begun to be performed by using a noncontacting temperature sensor. The clinical meaning of an eardrum temperature will be mentioned. A body temperature means a core temperature at which homeostasis is held in a living body, and a hypothalamus is considered to be the center for regulating this core temperature. From an anatomical viewpoint, an internal carotid artery perfused in the hypothalamus as the thermoregulatory center runs near an eardrum, which means that the eardrum and the hypothalamus share blood. It is therefore assumed that the correlation between the eardrum and the hypothalamus with respect to a temperature change is extremely high.
For this reason, the eardrum temperature has long attracted attention as a site reflecting the temperature of the hypothalamus as the thermoregulatory center of a living body. However, any conventional contacting clinical thermometer cannot measure the eardrum temperature, since thermometry using a contacting sensor may damage the eardrum. A radiation clinical thermometer using an infrared sensor has been proposed to eliminate this danger of eardrum damages and to make body temperature measurement within a short time period possible.
As shown in FIG. 13, however, a conventional noncontacting eardrum clinical thermometer making use of radiation has a wide field of view (V.sub.1) of an infrared sensor and an optical system associated with the sensor. Therefore, this clinical thermometer captures not only an eardrum V.sub.2 but also an external auditory meatus within the field of view of the infrared sensor. Note that the wide angle of field of the optical system means that an incident angle corresponding to an infrared incident sensitivity of 50% is larger than 0.586 .pi.sr (steradian), as a solid angle, with respect to the infrared incident sensitivity in the optical axis direction of the optical system. In this case, the optical axis of the optical system is generally in agreement with the normal direction of the light-receiving surface of the infrared sensor, and sr (steradian) is the unit of a solid angle. An angle (rad) on a plane is calculated as L/r by dividing the length L of a circular arc by its radius r. Likewise, the sr is calculated as A/R.sup.2 by dividing the area A on the surface of a sphere by the square of its radius R. 0.586 .pi.sr corresponds to .pi./4 rad as an angle from the optical axis, i.e., as a zenith angle viewed from the light-receiving surface of the infrared sensor.
As described above, the conventional noncontacting eardrum clinical thermometer using radiation has a wide angle of field of the infrared sensor, so the infrared sensor receives radiation energy as an average temperature of an eardrum temperature and an external auditory meatus temperature. This makes it impossible to measure a true eardrum temperature. In addition, even if it is possible to narrow the field of view of the infrared sensor and the optical system associated with the sensor, an eardrum exhibiting the highest temperature in an external ear is difficult to reliably capture in the field of view of the infrared sensor within a limited thermometric time. Consequently, it is difficult to reliably measure a true eardrum temperature.
An anatomical comparison of an external ear and an eardrum shows that venous blood heated or cooled in a head or the like is present in many sinus venosuses around an external auditory meatus. For this reason, the temperature of an external auditory meatus is readily influenced by an environmental temperature and therefore is not necessarily in agreement with the temperature of a hypothalamus as the thermoregulatory center. Therefore, the eardrum temperature including this external auditory meatus temperature cannot be said to be the core temperature of a living body in a true sense.
That is, the conventional noncontacting eardrum clinical thermometer using radiation has a wide field of view of the infrared sensor and the optical system associated with the sensor. Consequently, the conventional clinical thermometer senses the temperature including the external auditory meatus temperature susceptible to the influence of an environmental temperature, so this temperature is inadequate to be used as an indication of the eardrum temperature. In addition, the use of this temperature as a body temperature is also dangerous from a clinical viewpoint because the condition of a disease may be misread.